The National Social Life, Health and Aging Project (NSHAP) is a longitudinal study of older adults focused on mechanisms through which the trajectories of health and social connectivity are intertwined as people age. Data were first collected in 2005?6 (Cohort 1 Wave 1 or C1W1) from a probability sample of 3,005 community- dwelling adults born 1920?1947; these respondents were re-interviewed in 2010?11 (C1W2) together with their co-resident spouses or partners (N=3,377). In 2015?16 (C1W3), all surviving respondents were again re- interviewed and a new cohort of respondents born 1948?1965 during the Baby Boom was added along with their spouses/partners (C2W1). Together these data permit estimates for the entire population aged 50?95 in 2015 (N=4,777). Cohort 1 Wave 4 (C1W4) is scheduled for 2020?21 (R01 AG043538). This proposal seeks funding to collect a second time point of data from the new cohort (C2W2) simultaneously with C1W4. Individuals born in different time periods can exhibit substantial differences in health at older ages which may have important consequences for clinical practice and health policy. NSHAP data currently available allow researchers to assess health on multiple dimensions across cohorts born from 1920 to 1965. The addition of a second time point for those born from 1948?65 during the Baby Boom will permit comparing health trajectories among this cohort to those for older cohorts; by beginning recruitment at age 50, this cohort will also permit measurement of earlier indicators of trajectories. NSHAP is uniquely suited to comparing cohorts with respect to the rates of change in intimate and other social relationships (including explicit changes in social networks) and in health outcomes critical at older ages such as sensory and cognitive function (including Alzheimer's disease and related dementias), physical activity and function, sleep quality, sexual health and medication use. Moreover, NSHAP is unique in permitting the study of social and health trajectories within the context of the spouse/partner relationship, and C2W2 will double the number of couples for whom we have data for multiple timepoints. This proposed return visit to the younger cohort provides an opportunity to develop a flexible, robust platform for multimode data collection with the aim to reduce field costs and ultimately allow an increased frequency of contact with respondents, including the potential for targeted data collection following a specific health event. The proposed research involves substantial innovation in methods of and approaches to data collection, which will benefit both NSHAP and the field as a whole. We also propose innovative additions to NSHAP's questionnaire content and design, including questions on opioid use, the use of social media, a biological assay for HPV, and enhancement of cognitive assessment with information on response times that may also be obtained over the phone. To enhance the use of these data, which we shall make publicly available, we will solicit contributions to and edit a special issue of the Journal of Gerontology: Social Sciences focusing on cohort differences in social relationships and health trajectories.